This invention relates to a conforming body support with an air core.
In such a body support in the form of a mattress, an air core is used to obtain good conformity to the body of a user lying on the mattress. This principle, however, can also be used for other body supports, such as seat cushions and pillows. In comparison with, for instance, a water bed, the advantage is obtained that the mattress is considerably lighter does not need to be heated, involves less after-undulation, and that in case of leakage no water damage occurs.
International patent application WO 93/21803 discloses such a body support, having an outer contour and, within that outer contour, an air core, a side edge portion, contiguous to the air core, from a compliant filling material, and a bellows, integrated into that side edge portion, which in a condition of rest is airtightly separated from the air core and has compliant filling material in an inner space. The body support further comprises a system of passages which connects the bellows with the air core and connects the bellows and the air core with the surroundings, and a valve system for blocking, at least in the condition of rest, air flow from the air core.
For the air pressure in the air core--which, in practice, like a pneumatic tire, is not absolutely airtight--to be kept at a constant level, in mattresses according to this document the bellows are coupled to a buffer reservoir, Arranged between the buffer reservoir and the air core is a settable pressure reducing valve, which allows air to pass from the buffer reservoir to the air core if the overpressure in the air core relative to the surroundings decreases below a particular value. This means that the air core is replenished from the buffer reservoir depending on the pressure in the mattress in unloaded condition, In loaded condition the pressure in the air core is higher than in unloaded condition. The pumping of air to the buffer reservoir in use occurs automatically by compression and expansion of bellows, incorporated into the aide edge, when sitting down on the edge of the mattress, for instance when getting into and out of bed.
A drawback of this body support is that the buffer reservoir must be pumped up against an elevated overpressure, so that the bellows constitute relatively stiff elements in the edge of the body support, which feel unpleasant when sitting down on the edge of the body support, and which further have an adverse effect on the lying or sitting comfort in the edge area of the body support. Furthermore, the bellows and the buffer reservoir are subject to heavy loads when the mattress is used roughly, for instance when children jump or dive on it, especially when the pressure in the buffer reservoir is high. Preventing damage to the bellows therefore requires a robust construction.
The overpressure in the air core is very low in unloaded condition and is influenced by objects lying on the bed such as blankets and/or quilts, as well as by fitted sheets stretched onto the mattress. The overpressure in the air core in unloaded condition is therefore difficult to control and, owing to the disturbances referred to, less suitable as a measure for the hardness of the mattress. Finally, with such a mattress, getting into and out of bed is often accompanied by attendant noises due to the air displacement from the bellows to the buffer chamber.
International patent application WO 95/09552 discloses another body support with an air core, designed as a mattress, in which the bellows are formed by a corner area of the air core, The bellows communicate via a permanently open aeration opening with the rest of the air core. This aeration opening is so small that air flowing back through it does not substantially slow down inflation. The suction passage for admitting air to the bellows is intermittently closed of f during pumping by the user who places the member of his body with which he compresses the bellows, in front of the suction opening. After inflation of the air core the suction passage is closed hermetically and a residual pressure difference between the bellows and the rest of the air core is equalized via the aeration passage.
Although the pressure in the bellows-shaped portion of the air core in the condition of rest is basically equal to the pressure in the rest of the air core, the spring characteristic of the bellows-shaped portion of the air care differs considerably from the spring characteristic of the rest of the air core. Upon compression of the rest of the air core, air is displaced. Displacement of air, upon compression of the bellows portion of the air core, is to proceed via the aeration passage and the pumping passage. For the purpose of rapid displacement of air, the aeration passage cannot play a significant role because otherwise the air core would deflate too fast during inflation. If the pumping passage is small, hardly any air can be displaced upon loading of the bellows portion. The bellows portion of the air core is then relatively hard and the bellows are heavily loaded upon strong local compression. If, conversely, the pumping passage is large, a reasonable volume of air is displaced, but after compression of the bellows it takes quite some time for the shape thereof to be restored again, since via the aeration opening per unit of time only little air can flow to the bellows portion.
Further, regulating the pressure of such mattresses is laborious because the suction passage must each time be closed off with a cap prior to test-lying.